Hand trucks and carts are used to transport a wide variety of objects such as boxes, gas cylinders, welding equipment, tools, mechanical parts and other items. Most of these hand trucks are either a 2-wheel design or a 4-wheel design. However, some hand trucks can convert from a 2-wheel configuration to a 4-wheel configuration.
An example of a known 2-wheeled hand truck is disclosed in U.S. Pat. No. D273,522. With such a 2-wheel hand trucks, an operator of the 2-wheel hand truck maintains a main frame of the 2-wheel hand truck in a tilted orientation with respect to the ground (e.g., at approximate a 45-degree angle) when carrying a load on a load platform (i.e., a load support structure) of the 2-wheel hand truck. As such, a load carried on the load platform of a 2-wheel hand truck is always partially supported by the operator when the 2-wheel hand truck is in its mobile (i.e., tilted) position. The need for the operator to partially support the load when a 2-wheel hand truck is in a mobile position can result in the operator becoming strained and/or fatigued. It also means the operator's hands are not free for other tasks, such as opening doors, ensuring the load remains securely positioned on the load platform, etc.
The objective of maintaining a 2-wheel hand truck in a tilted orientation is to position a center of gravity of the load over the rotational axis (e.g., axle) of the wheels. Positioning the load in such a manner minimizes the effective weight that the operator is supporting. However, the shape of the load and/or it's position on the load platform can dictate its center of gravity relative to the location of the load on the load platform, thereby reducing the “leverage effect” provided by a 2-wheeled hand truck. Similarly, it is not always practical or possible for an operator to maintain a 2-wheel hand truck in an optimized tilted position (e.g., during certain maneuvers, when traversing certain obstacles (e.g., stair), etc). As such, an optimized leverage effect of a 2-wheel hand truck can be highly independent of a tilt angle preferred or required by an operator.
In an effort to overcome limitations and drawbacks of 2-wheel hand trucks, various 4-wheel hand trucks have been devised. Such 4-wheel hand trucks support an entire portion of a load when in a mobile position. However, the wheelbase of a 4-wheel hand truck is generally fixed, thereby making them less maneuverable than a 2-wheel hand truck. Furthermore, the frame structure of a 4-wheel hand truck is typically more cumbersome and/or complex than a 2-wheel hand truck. Still further, 4-wheel hand trucks can be less useful when certain obstacles/situations present themselves (e.g., traversing stairs). An example of a known 4-wheeled hand truck is disclosed in U.S. Pat. Nos. 5,277,439 and 6,848,881.
In an effort to overcome limitations and drawbacks of 2-wheel hand trucks and 4-wheel hand trucks, 2-to-4 wheel convertible hand trucks have been devised. In one manner or another, these 2-to-4 wheel convertible hand trucks can be selectively configured and/or used as a 2-wheel hand truck or a 4-wheel hand truck. When in a 2-wheel configuration, a load can be supported in much the same manner as with a 2-wheel hand truck, as discussed above. When in a 4-wheel configuration, a load can be supported in much the same manner as with a 4-wheel hand truck, as discussed above. Many of these 2-to-4 wheel convertible hand trucks require latching mechanisms or can require reconfiguration of the hand truck's frame for switching between 2-wheel operation and 4-wheel operation. Furthermore, conversion between wheel configurations can sometimes require that there is no load on the hand truck (e.g., secondary wheels are not attached to the main frame in such a way that they pivot freely). Still further, when in the 4-wheel configuration, the wheelbase is generally a relatively long (e.g., extended) and there is not a secondary 4-wheel configuration short wheelbase use configuration. As such, 2-to-4 wheel convertible hand trucks are often cumbersome to provide both 2-wheel and 4-wheel operations, which can be a considerable disadvantage in situations where a load is being moved across a flat surface and then needs to be transported over obstacles (e.g., up or down stairs). Examples of such known 2-to-4 wheel convertible hand trucks are disclosed U.S. Pat. Nos. 3,647,236; 4,921,270; 5,207,439 6,308,967; 6,328,319; and 6,364,328.
Therefore, a hand truck offering 2-to-4 wheel conversion functionality in a manner that overcomes shortcomings associated with prior art hand trucks would be advantageous, desirable and useful.